1. Field of the Invention
The present invention relates generally to a method and system for detecting elevated intracranial pressure. Specifically, embodiments of the present invention relate to using venous pulsation signals obtained from a patient's forehead to non-invasively detect elevated intracranial pressure. Further, some embodiments are directed to quantifying intracranial pressure based on a pressure or elevation required to overcome the venous pulsations.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The human skull is essentially a rigid fluid-filled container. Principle constituents within the skull include brain tissue, blood, and cerebral-spinal fluid (CSF). Because the skull is essentially rigid and has a constant volume, if there is an increase in the volume of the contents of the skull, the pressure inside the skull (i.e., intracranial pressure) will rise unless some fluid is able to escape. For example, if the brain tissue experiences swelling, a certain amount of blood or CSF must escape the skull cavity to prevent a rapid increase in pressure. During such swelling, pressure inside the skull may rise above the normal range. Further, if swelling continues until little or no fluid remains, any further swelling will cause a rapid increase in intracranial pressure (ICP). It should also be noted that obstruction of fluid flow out of the skull (e.g., obstructed venous outflow) can increase ICP because the fluid flowing into the skull will build pressure therein.
ICP is measured in millimeters of mercury (mmHg). The normal range for ICP values is from around 5 mmHg to around 13 mmHg. American and European head injury guidelines recommend that actions be taken to treat ICP when it is above 20-25 mmHg, as elevated ICP is a potentially life-threatening condition. Treatment of elevated ICP typically begins with administration of drugs to reduce systemic fluid volume or blood pressure. If the elevated ICP is not detected early enough, part of the skull may need to be removed to relieve the pressure.
While elevated ICP is often a result of trauma, the elevated pressure itself can cause damage to the central nervous system by compressing important brain structures and restricting blood flow through vessels that supply the brain. Elevated ICP typically occurs as a result of increased volume within the skull cavity. For example, elevated ICP occurs acutely in head trauma cases involving cerebral edema, which is also referred to as brain swelling. Elevated ICP may occur more gradually in cases of hydroencephalitis (i.e., water on the brain) or brain tumors. Other conditions that may cause elevated ICP include: subdural hematoma, encephalitis, meningitis, hemorrhage, stroke, and so forth.
Traditional techniques for monitoring and measuring ICP generally involve the use of invasive devices. For example, commonly used devices include hollow screw and bolt devices. These typically include metallic cylindrical instruments which are inserted into the patient such that an instrument tip protrudes into the subarachnoid space to facilitate pressure measurement. The subarachnoid space is the compartment within the skull and spinal column that contains the CSF. Another commonly used invasive device for ICP monitoring is an intraventricular catheter. The intraventricular catheter is typically placed inside ventricles (i.e., fluid filled cavities) of the brain to facilitate pressure monitoring. Insertion of such invasive devices (e.g., hollow screws and catheters) to facilitate ICP monitoring can be dangerous. For example, insertion of a monitoring device through a patient's skull may cause hemorrhaging or infection.
Some existing techniques for monitoring ICP are non-invasive. For example, some existing methods involve emitting ultrasound into the patient's brain to facilitate detection of an elevated ICP. Such utlrasound emissions typically reach the brain through natural windows in the skull. For example, ultrasound emissions may be introduced to a patient's brain via an eye socket. However, these ultrasound emissions may be undesirable depending on how long the eye must be esonified. Further, sensor placement for such methods can be difficult, resulting in inaccuracies.
Accordingly, it is desirable to provide an improved non-invasive monitoring device for detecting and/or measuring ICP that facilitates early detection of elevated ICP.